1. Field of the Invention
The present invention relates to an image measuring apparatus that measures the shape of an object to be measured, by emitting light to the object to be measured and imaging the object to be measured.
2. Description of the Related Art
Conventionally, a shape measuring apparatus has been known that measures the surface shape of an object to be measured by scanning the surface of the object to be measured by a probe and acquiring the positional coordinates and the like of each part of the object to be measured. As such a shape measuring apparatus, a noncontact type is known that performs measurement without bringing a probe into contact with the surface of an object to be measured by means of an optical system as in JP-T-2009-534969.
In the noncontact-type surface shape measuring apparatus described in JP-T-2009-534969, linear laser is emitted to the object surface by a scanning probe and this is imaged from a predetermined angle with respect to the laser emission direction to thereby measure the surface shape of the object. With this noncontact-type surface shape measuring apparatus, there is no possibility that the object surface is flawed, and it is unnecessary to consider the influence of the probe wear on the measurement accuracy.
In such a noncontact-type surface shape measuring apparatus, when the object surface is imaged in a case where the reflectance of the object surface, the relative angle between the optical probe and the object surface, and the like are finely changed, an insufficiency of light amount and an excess of light amount occur. That is, in low-reflectance parts, the emitted laser light is hardly reflected and this makes the observation by light receiving elements difficult, and in high-reflectance parts, saturation (excess of light amount) occurs.
To solve this problem, the invention described in JP-T-2009-534969 takes the following measure: When the object surface is imaged, one-dimensional images in a direction perpendicular to linear laser light are successively taken along the laser light, and at the same time, the output of the laser device is adjusted according to the maximum brightness in the one-dimensional images. This method enables the laser-irradiated object surface to be imaged with an appropriately light amount.
However, with this method, since no reflected light is detected when parts not reflecting laser light (e.g. a part where no object to be measured is present in the measurement range and a part hidden by bumps and dips) are imaged, the laser device always operates at maximum output. In such a case, there is a possibility that a thermal drift or a malfunction occurs due to the heat generation of the laser, and even if a cooling fan is attached, the vibration by the cooling fan is transmitted to the probe and this can degrade the measurement accuracy.
Moreover, in such a case, it is necessary to provide the measurement probe with an air hole for cooling, and this leads to deterioration of the environment resistance. Further, the laser light source deteriorates faster, and power consumption is high.